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Assessment of damage by greenbug (Homoptera:Aphididae) to mixtures of resistant and susceptible Sorghum, Sorghum Bicolor (L.) Moench, hybrids as affected by natural enemies
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Greenbug, Schizaphis graminum (Rondani), is an important insect pest of sorghum, Sorghum bicolor (L.) Moench, in the United States. An integrated pest management (IPM) approach has been used to manage greenbug. Greenbug biotype formation renders resistant sorghums ineffective as an IPM component. Multilines have been used to prolong duration of resistance genes for pathogens in small grains and may contribute to the effective management of greenbug biotypes. Five biotype E greenbug resistant and susceptible sorghum genotype mixtures were studied. These mixtures were evaluated in greenhouse experiments from 1993 to 1995 and field experiments on the Texas A&M University Research Farm near College Station, TX during 1994 and 1995. Greenhouse experiments assessed effects of mixtures on greenbug and field experiments evaluated mixture effects on greenbug in the presence and absence of natural enemies. Effects were measured by assessment of greenbug abundance, vegetative response, and grain yield data. Greenbug abundance trends in greenhouse experiments suggested plant mixtures containing 25% or less resistant plants were less effective for managing greenbugs than those mixtures containing at least 50% resistant plants. Plants of all mixtures were statistically equal for plant height and insect damage. Data. indicated plant height may have confounded results in the greenhouse experiments. Considering plant height results, mixtures containing 75% resistant plants may be equal to sorghum stands of all resistant plants for greenbug management in seedling sorghum. Greenbug abundance was significantly reduced in treatments where natural enemies were allowed access, suggesting natural enemies prevented greenbug from reaching economic levels in field experiments. Greenbug abundance and plant damage data indicated a plant mixture containing 25% resistant plants was least effective managing greenbug. Treatments which allowed natural enemies access to greenbug had significantly taller plants, greater plant masses, and grain yield than those in which natural enemies were excluded. Plant height, plant mass, and grain yield data were inconclusive for determining statistical differences between mixtures. Experiments do suggest mixtures containing a minimum of 50% resistant plants may be as effective as all resistant stands experiencing moderate greenbug pressure.
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Stewart, Klint Gilbert (1996). Assessment of damage by greenbug (Homoptera:Aphididae) to mixtures of resistant and susceptible Sorghum, Sorghum Bicolor (L.) Moench, hybrids as affected by natural enemies. Master's thesis, Texas A&M University. Available electronically from
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